The invention relates to a pump, in particular a vane pump, for a liquid or gaseous medium and particularly the sealing of the pressure chamber and the operating chamber of the pump.
Known pumps of this type are used, for example, for power steering systems in a motor vehicle. They comprise an operating chamber, which is closed in the axial direction by means of at least one pressure plate. Arranged in the operating chamber is a rotor, which can be coupled to the drive shaft of an electric motor. A separate mounting for the rotor is not provided, as the rotor is mounted exclusively via the drive shaft. This configuration, however, produces large external diameters for the at least one bearing of the drive shaft and a shaft sealing ring which seals off the electric motor with respect to the pump in the area of the drive shaft.
On the lateral face facing away from the rotor, the pressure plate is in contact with a pressure chamber, which is sealed off with respect to the motor by a coupling element that cooperates with at least one seal and surrounds part of the drive shaft. The coupling element engages over an annular flange on the pressure plate, which flange is provided on the side facing away from the rotor and has a greater external diameter. As a result, between the flange and the coupling element, a radially inner sealing face is formed which divides the pressure chamber from the pump unit and whose distance from the axis of rotation of the drive shaft is large. The arrangement of the inner sealing face also determines the distance between the pressure chamber and the axis of rotation of the drive shaft, which is accordingly very large. As a result, the external diameter of the rotating group has to be configured in a correspondingly large manner.
It is therefore an object of the invention to provide a pump of the type mentioned at the beginning in which a more compact design, in particular a pump unit with a small external diameter, can be implemented.
In order to achieve this object, a pump having the features of the invention is distinguished by the fact that the coupling element has a sleeve-like section which engages in the through opening in the pressure plate. The distance between a radially inner sealing face of the pressure chamber and the axis of rotation of the drive shaft between the coupling element and the through opening in the pressure plate is therefore only very small, so that a pump unit having the pressure plate and the rotor can be implemented with a small external diameter. As a result, a pump with a compact, space-saving construction can be provided.
According to a development of the invention, the diameter of the through opening made in the pressure plate is smaller, preferably considerably smaller, than the external diameter of a shaft sealing ring surrounding part of the drive shaft. Since the shaft sealing ring must not be connected to the pressure chamber, a radially outer sealing face of the pressure chamber is arranged at a great distance from the drive shaft, on account of the large external diameter of the shaft sealing ring. The area located between the radially inner and the outer sealing face is advantageously covered in a sealing manner with the aid of the coupling element. According to a first design variant, for this purpose the coupling element has a collar which accommodates the shaft sealing ring and reaches beyond the section of the casing, preferably at least one second seal, for example an O ring, being provided in order to seal a gap between the collar and the section of the casing. In another design variant of the pump, the coupling element cooperates with an end face of the section of the housing that accommodates the shaft sealing ring, that is to say it does not have a sealing collar but preferably bears with a lateral face facing away from the rotor on the end face of the section of the casing. In order to seal the gap between the coupling element and the end face of the section of the casing, in one advantageous embodiment at least a third seal, for example an O ring, which can be arranged in a groove in the end face, or a sealing disk is provided. In a further design variant, the coupling element engages with its collar in a recess in the section of the casing in which the shaft sealing ring is arranged, it being possible for the gap between the outer circumferential face of the collar and the wall of the recess to be sealed, preferably by means of a third seal.
In a preferred embodiment, there is a clearance connected to the pressure chamber between the coupling element and the pressure plate. On the basis of this configuration, it is possible for the entire projected lateral face, facing the coupling element, of the pressure plate to be acted on by the medium under pressure, for example oil, as a result of which the pressure plate is preferably pressed against a contour ring surrounding the operating chamber. Applying pressure to the entire lateral face of the pressure plate means that deformation of the pressure plate in the manner of a disk spring, which could lead to a short circuit between an inlet zone and a delivery zone of the pump, is prevented. In order to act on the pressure plate with a force oriented in the direction of the rotor, instead of the clearance or in addition to the clearance connected to the pressure chamber, a pressing device can be provided which, for example, comprises at least one disk spring. The pressing device is particularly advantageous when the coupling element is so configured that it cooperates with the end face of the section of the casing that accommodates the shaft sealing ring.
In addition, preference is given to an exemplary embodiment of the pump in which, in the area between the larger-diameter collar and the smaller-diameter section engaging in the through opening in the pressure plate, the coupling element has an annular bead, which is used to stiffen the coupling element. This makes it possible to form the coupling element with a thin wall.
Furthermore, preference is given to an exemplary embodiment of the pump which is distinguished by the fact that the coupling element consists of sheet metal and is preferably formed in one piece. The coupling element formed as a sheet-metal molding can therefore be produced cost-effectively. Of course, the coupling element can be produced from virtually any material which, for example, can be corrosion-resistant and whose strength properties are sufficient to withstand the pressure in the pressure chamber. Since the coupling element is located in the pressure chamber or adjoins the latter, in the case of a vane pump used to deliver oil, the coupling element can also consist of a metal susceptible to rusting, since the coupling element is protected against corrosion by the oil.
Further advantageous embodiments emerge from the other subclaims.